1. Field of Invention
This invention relates to pedometers, specifically to pedometers that measure the stride length of the wearer.
2. Description of Prior Art
Pedometers are devices for measuring the distance traveled by a person when walking and running. By using a device for measuring time in conjunction with the pedometer, the elapsed time taken to travel a distance can be measured and the average speed can be determined by dividing the distance traveled by the time taken to travel that distance.
In most of the prior art, pedometers do not determine the length of each individual step, but instead rely on a preset average stride length of the wearer. These pedometers count the number of steps and then compute the distance traveled by multiplying the step count by the preset average stride length. The accuracy of these pedometers depend on accurately counting the number of steps taken and accurately setting the preset stride length to the average stride length actually taken by the user. Since the stride length can vary greatly for different walking speeds and gaits, this method can be very inaccurate unless the person is careful to maintain the particular speed and gait that yields the preset average stride length. Running gaits vary even more widely in stride length than walking gaits and thus this method cannot accurately compute the distance traveled by runner.
Pedometers count the number of steps taken by the wearer using a variety of methods. Typical pedometers sense the up and down motion of the wearer caused by each stride by means of a weighted pendulum. The inertia of the pendulum causes it to move with relation to the pedometer. In mechanical pendulums, this motion is typically sensed using a ratchet mechanism, which advances a counter with each swing of the pendulum. (See U.S. Pat. No. 4,560,861 to Kato, et. al., Dec. 24, 1985.) Electrically instrumented pendulums typically use a switch contact which is closed by each swing of the pendulum. (See U.S. Pat. No. 5,117,444 to Sutton, et. al., May 26, 1992.) In either case, the pedometer must be adjusted according to the stride characteristics of the wearer. Some pedometers have a switch that can be set to "walk" or "run" while others allow a range of adjustments. A drawback to pedometers that rely on pendulums is this requirement that they be adjusted to the user's gait. This means that the wearer must maintain approximately the same gait or the pedometer will not count the steps taken by the user accurately.
Some pedometers count steps more directly by means of a sensor or sensors embedded in the shoe that are connected directly to a counter. This can be done mechanically where each step depresses a mechanism that causes a mechanical counter to increment. More frequently electrical means are used whereby an electrical switch is closed by each step, creating an electrical signal that causes an electronic counter to increment. (See U.S. Pat. No. 5,640,786 to Buyayez, Jun. 24, 1997.) This method counts the number of steps more accurately than pedometers that rely on pendulums. In particular, these pedometers allow the user to change gaits while walking and running. However, the accuracy of these pedometers is still limited to the accuracy of the preset stride length.
Some recent pedometers do not rely on a preset stride length, but use the rate at which steps are taken to estimate the length of each stride. (See U.S. Pat. No. 5,583,776 to Levi, et. al., Dec. 10, 1996.) The stride length is correlated to some extent to the step rate, but this correlation does not hold for different gaits and is not generally accurate for running speeds greater than 7 or 8 m.p.h. U.S. Pat. No. 5,583,776 further discloses a pedometer that incorporates an accelerometer, which is used as a more accurate alternative to the pendulum mechanism of ordinary pedometers. This patent discloses two methods for counting the number of steps taken. One method detects peaks in the acceleration data measured by the accelerometer which correspond to individual steps taken. A second method uses signal processing algorithms to extract the fundamental step frequency from the accelerometer data. The number of steps taken is then calculated by multiplying the elapsed time by the step frequency. The step frequency is also used to estimate the average stride length, relying on the correlation between step frequency and stride length. In this regard, U.S. Pat. No. 5,583,776 is similar to other prior art because it counts the users steps and estimates the stride length from the rate at which steps are taken. In particular, it does not measure the acceleration of the foot itself, and provides no advantage over other prior methods for counting steps or estimating stride length.
U.S. Pat. No. 4,371,945 to Karr, et. al., Feb. 1, 1983 discloses a device that directly measures the stride length by means of an ultrasonic distance measuring device that measures the distance between the wearer's feet when taking a step. This requires an ultrasonic transmitter strapped to one leg and an ultrasonic receiver strapped to the other leg, each connected to a processor that performs the distance calculation. This device is both cumbersome for the user to wear and more expensive than ordinary pedometers because of the ultrasonic devices required. U.S. Pat. No. 4,703,445 to Dassler, Oct. 27, 1987 discloses a device that operates in a similar manner using ultrasonic transmitters in both shoes.
U.S. Pat. No. 4,736,312 to Dassler, et. al., Apr. 5, 1988 discloses a device that measures the stride length of a runner by measuring the elapsed time between the time when one foot lifts off the ground and the time when the other foot hits the ground during a stride. This provides a more accurate estimation of stride length than possible using the step frequency alone. However, the shoes on both feet are equipped with sensors, and the data from both must be communicated to a central processor which performs the distance calculation. Thus this arrangement is not a self-contained unit that can be worn by the user. Since it is comprised of three different components, it is also more expensive to make than a single unit.
U.S. Pat. No. 5,485,402 to Smith, et. al., Jan. 16, 1996 discloses a gait activity monitor that records the number of steps taken by the wearer. This monitor incorporates an accelerometer attached to the ankle of the wearer, which measure the acceleration of ankle. A data processor processes this acceleration data, counting and recording the number of steps taken during each measurement time interval. This monitor, however, does not calculate any distance traveled. Moreover, it is not a self-contained unit that the user can portably wear.